Finding Spicebush & Papilio troilus Larvae

We have finally found a good source of spicebush (Lindera benzoin) trees; we also able found spicebush swallowtail (Papilio troilus) larvae on these trees. 

---

When we first visited the Cornell Botanic Garden about a week ago on August 21, we were perplexed to find a female spicebush swallowtail (Papilio troilus) sucking nectar near the entrance but no spicebush (Lindera benzoin) or other host plant anywhere in the garden. Although the online plant database for the Cornell Botanic Garden lists spicebush very close to the section that we visited, it appeared that the online map and the map at the actual garden were not quite the same (the former is probably outdated) and we were unable to find the spicebush that is supposedly there. To make extra sure, we eventually asked a garden employee who confirmed that there was indeed no spicebush at this part but that there was spicebush at a far away (well, by that we mean by foot) arbetorium. 

Yesterday, we spent the entire afternoon trying to get to the arboretum, but ended up taking a few wrong turns that made the trip so unnecessarily long that by the time we ended up at some form of an entrance, it was late in the day and we were very tired. We still took a brief look at some of the trees there, but we were only able to find some Prunus species, Japanese corktree (Phellodendron japonicum) (this is Rutaceae, but doubtful that Papilio cresphontes utilizes it; even if it does, the tree was far too large to search), and some other irrelevant things. The arboretum is actually a very enormous place, so we figured we would need to use the online database if we were to ever find anything specific, assuming that the database is still mostly accurate. 

Today, we walked to the same entrance we were before, but turned to the right side of the street in accordance to the database to a section called the Mundy Wildflower Garden which we quickly realized was chalk full of spicebush trees (perhaps that is an exaggeration. . . there were probably only a little more than a dozen or so). There were large and small trees, some with mounds of fruit, that were growing in all types of different locations; some were in the shade, some in the sun, and some were isolated by themselves. At some point we saw a Papilio troilus adult fly by, which reassured us that the Papilio troilus population was real (that the female from before was not some kind of fluke) and that they were actually utilizing these spicebush trees. However, it took us almost an hour of checking the trees before we found our first larva, which was a second instar hidden in a tightly rolled up characteristic leaf nest on a very young, isolated tree in open sun. We simply had not developed an eye for these nests, but after finding this first larva we were very quickly able to locate a second one, this time a third instar, on a different small tree located in the shade. There also happened to be a huge sassafras (Sassafras) in the garden, but because it was so large and tall, we were not able to check it thoroughly and did not find anything on it. We were surprised that we were not able to find more larvae or any eggs, but that may be because the season is coming to an end; certainly, this is constitutes the last flight and the last brood of the year. ​

As this is our first time seeing Papilio troilus larvae in real life, we can't help but be bewildered by their appearance. While a lot of other immature swallowtail larvae are smooth and shiny, these larvae are especially so, giving off a slick, glossy sheen in light. They, of course, are bird dropping mimics with the orangish brown base color and white saddle and rear end but they also already have large black eyespots on their thorax. They have light orange head capsules, a yellow orange osmeterium, and the two rows of dorsal abdominal spots can already be seen. The glaucus group larvae do not get noticeable eyespots or abdominal spots until the third instar, are darker in base color, tend to have a lot more white, and have dark colored head capsules, making it seem like the troilus are ahead of the game in abandoning the bird dropping appearance for snake mimicry. The troilus also have a much more smooth coloration (not at all mottled) and the thorax is wide and flat rather than just a thick ball as in the glaucus group, a feature that will become much more obvious in later instars. In many ways, from the leaf nests to the almost comical appearance, the troilus larvae can be seen as a more extreme version of glaucus group larvae. 

The troilus larvae eat in a strange fashion. For most of the day, they obviously rest inside their leaf nest, but when they are hungry, they crawl out and make messy, sometimes tunnel-like holes starting from the place that they cut out the leaf for the nest. Much of their frass is contained inside the nest.

After bring them home, we had to disturb them out of their nests in order to change out the leaves for fresher ones, which is very stressful for the larvae that seem to have a very hard time re-making the nest. Instead, we have found that the larvae like to wonder off the leaf and onto the side of the container to rest, which is the same behavior we saw in P. rutulus. 

---

Authors
Brian Liang

---